Usually, the design of a circuit board has been performed with computer aided design (CAD). With the above-mentioned design which is referred to as the packaging design CAD (or the layout CAD), a computer arranges wiring with interactive processing and/or automatic processing on the basis of circuit-connection information (a net list) or information about a component to be mounted on the circuit board to obtain a desired circuit function.
After finishing the packaging design, the circuit board is generated on the basis of CAD data. Before generating the circuit board, the CAD data is often subjected to a structural analysis simulator to confirm the mechanical strength of the circuit board. For example, it is confirmed, on the basis of the analysis result, whether the strength of the bonding part of the mounted component is impervious to a stress applied to the circuit board when the circuit board is handled and provided in a cabinet.
In the field of the above-mentioned structural analysis, an analysis method based on the finite element method has been available. According to the above-mentioned method, a three-dimensional model to be analyzed is mesh-divided, that is, divided into a set of elements with small regions, and the entire behavior is predicted on the basis of the behavior of each of the elements with the small regions. Therefore, in general, two-dimensional CAD data of the circuit board, which is generated with the packaging design CAD, is converted into three-dimensional model data (hereinafter, the model data is often referred to as a model), and the three-dimensional model data is subjected to the structural analysis simulator. At that time, it is assumed that no bonding material such as solder is used for the part where a pad of the circuit board is bonded to an electrode of the mounted component, that is, the bonding material is ignored. Otherwise, a circular cylinder or a prism is generated as a simple bonding model and added to the three-dimensional model of the circuit board. Then, the three-dimensional model is subjected to the structural analysis simulator. FIG. 8A illustrates a three-dimensional model of a finished circuit board having components that are mounted on the circuit board on the basis of two-dimensional CAD data of the circuit board. Pads 11 to be bonded to mounted components are provided on a circuit board 10, and a ball grid array (BGA) type component 20, a chip type component 30, and a quad flat package (QFP) type component 40 are arranged over the pads 11 as the mounted components. The two-dimensional CAD data does not include data related to the shape of a bonding material such as solder used to bond the pad 11 to the mounted components. Therefore, the mounted components are arranged and floated above the pad 11 by as much as a specified amount determined to be the thickness of the bonding material. FIG. 8B illustrates a case where simple bonding models 50, 51, and 52 are added to the three-dimensional model illustrated in FIG. 8A. The simple bonding model denotes a bonding model including a bonding material such as solder having the shape of a circular cylinder or a prism. Traditionally, the above-mentioned simple bonding model has been used to perform a structural analysis. FIG. 8C illustrates a case where the bonding model is omitted and the mounted components are directly bonded to the pads 11. Traditionally, a mechanical simulation has been performed on the three-dimensional model illustrated in FIG. 8B or FIG. 8C.
FIG. 8D illustrates examples of actual shapes of bonding parts 60, 61, and 62 where the pads are bonded to the mounted components. That is, the actual shape of the bonding part is significantly different from that of the simple bonding model.
In a related matter, the following technology of generating an analysis model of a bonding part has been available. When first and second structural members are bonded to each other with a bonding member which is a third structural member having small thickness, a first and second bonding points are provided on the first and second structural members, respectively, where the first and second structural members are bonded to the third structural member at the first and second bonding points, respectively, and the first and second bonding points are restricted in accordance with a relation achieved on the basis of the physical property of the third structural member. Japanese Laid-open Patent Publication No. 2009-3529 discloses a related technology.